That's something I've been considering too. We're exploring space but haven't fully explored our own oceans. If something can move fast deep underwater, just think how fast it could be in a nitrogen/oxygen-based atmosphere. Plus, if something can stand the pressures of the oceans' depths, it maybe be able to easily cope with G-forces that would kill any of us. That breaking-the-sound-barrier-without-a-sonic-boom thing has me puzzled though.